I certainly defer to you, Petr. I got into this discussion because I was curious as to why this didn't seem to work for me: or at least only occasionally worked. I may have misinterpreted some of what I read, or the writers did. It seems many of us get higher FG readings with hydrometer than any of the formulas predict. As I said, I don't need a refractometer except pre-boil. For those who do, I hope they find your formula serves their needs. It's astonishing how many times essentially this same conversation has been repeated on various forums. It seems there is great interest in refractometers, but a few intractable gremlins in the works! Carry on the good work. BTW I appreciated your recent article on hop utilization, too.